Week 2: How to Build a Planet: formation of stars and galaxies Flashcards
What is a star?
-large glowing ball of gas
-generates heat and light through nuclear fusion
How did the first stars form?
1 .normal matter (hydrogen and helium) accumulate and form clumps
2. The clumps accumulate and contract and heat up under their own gravity.
3. T of core increases to point of hydrogen fusion
4. Pressure from gas density and radiation reach equilibrium with gravitational forces
5. causing collapse
What are Population III stars?
first stars that ever formed
-short lived
-supermassive
Sun is a population I star formed around 4600Ma
How can we distinguish Population III stars from later stars? What is the evidence that our Sun is a third-, fourth, or fifth-generation star?
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Our sun is a main sequence star because of its luminosity and temp
3rd generation star
What are the stages in the lifecycle of a sun-sized star? What is the relationship between contraction and expansion? Where in its lifecycle is our sun?
- dust and gas
2.protostar
3.main sequence star(sun is at this stage)
4.Giant star
5.Variable stage
6.Nebula - White dwarf
8.Black dwarf
sun= main sequence star
balance between expansion (promoted by fusion reactions) and contraction (due to gravity)
The first elements (hydrogen and helium) formed within minutes of the Big Bang. How did the other elements form? ie elements up to iron with an atomic number of 26 and elements with atomic numbers greater than iron?
Neutron or Proton Capture
What is stellar nucleosynthesis?
Fusion in massive stars
Fusion of elements lighter than iron=release energy to generate nuclei with greater binding energy
Fission of elements heavier than iron= release energy to generate nuclei with greater binding energy
How do the processes that generate elements differ in sun-sized versus massive stars?
sun-sized stars= hydrogen burning process
massive stars= stellar nucleosynthesis
How does the end stage of a sun-sized star differ to the life cycle of a more massive star?
sun sized star= black dwarf stage
massive star= black hole or neutron star
What role did supernova explosions play in the formation of elements with atomic numbers greater than iron, the first galaxies and Population II stars?
supernova explosions expel heavy elements into space where they are incorporated into the gas that forms the next generation of stars.
First galaxies:
1.intense ultraviolet radiation emitted by Pop III stars reionized the surrounding medium
2. shock waves from these stars compressed surrounding ionised gas= triggering a burst of star formation
3. black holes formed from core collapse
4. ongoing gravitational collapse around these= formations of first galaxies by 400myr
What is the origin of black holes? What is their relationship to galaxies?
the core of a star that has undergone a supernovae explosion collapses
if its over 25 solar masses= collapses to a black hole
ongoing gravitational collapse around these black holes= formations of galaxies
almost every large galaxy has a supermassive black hole at the centre
When was the period of most rapid galaxy merger?
around 800million years after the Big Bang (10,000 galaxies)
When was the period of highest star formation (when did star formation peak)?
11,200Ma ago
approximately 3.5Gyr (i.e. billion) years after the Bing Bang
How old is the Milky Way?
13.2 billion/13200Ma
How did it form?
1.began as several over-densities; globular clusters were seeded within these (13200Ma)
2.graviational attractions led to the merger of these over-densities; stars in the inner halo forming by 11500Ma
3.collapse of gaseous interstellar medium from spheroid shape-disc by 8800 +/- 1700Ma
